Heater



H0 @HO HEATER ATTOR E O. C. SCHAUBLE ET AL Original Filed Jan. 23

Il? Qi@ O owl/@HO Sept. 20, 1955 United States Patent O HEATER @tto C. Schauble, Mount Kisco, Valentine Mekler, Jackson Heights, Edward H. Palchik, Forest Hills, and Marcel 3. P. Bogart, Mamaroneck, N. Y., assignors to The Lummus Company, New York, N. Y., a corporation of Delaware Original application January 23, 1948, Serial No. 3,848,

now Patent No. 2,641,234, dated June 9, 1953. Divided and this application December 19, 1952, Serial No. 326,976

2 Claims. (ci. 122-235) This invention relates to improvements in heaters of the tubular type for the carrying out of chemical reactions by pyrolysis, and the present application is a division of our similarly entitled co-pending application Serial No. 3,848, filed January 23, 1948, now Patent No. 2,641,234 issued lune 9, 1953'.

The particular object ofA our invention is to ,provide a tubular heater having relatively high heat input rates in the reaction zonev which are substantially uniformv throughout 360 of the tube cross section as well as along the length of a tube section.

Another object of our invention is to provide an irnproved batile tile and tube construction which will provide for a high degree of reradiation of heat to the tube units.

A further object of our invention is to provide a tubular heater having independently red and controlled reaction sections and preheater sections in which the relatively cooled products of` combustion4 from -the reaction section are passed through bafe floor tile into the preheater section wherein they are further heated; by additional hot products of combustion generated in the preheating section for the desired heat transfer to the tubes therein.

A still further object ofthe invention is to provide `an improved method for thepyrolytic, treatment of light hydrocarbons or organic compounds in whichl improved control is provided for the rate of heat input and particularly of the residence time so that optimum yields of desired products may be obtained.

Further objects and advantages of our invention. will appear from the following description of a preferred form of embodiment thereof' and in which:

Fig. 1 is a substantially central vertical sectionthrough one unit of a multiple tubular heater.

Fig. 2 is a detailed and enlarged vertical cross section showing the bafe tile and tube construction. v

The heater or furnace contemplated isa substantially rectangular chamberconstruction havingk side walls 10, end walls 12, a iioor 14 and a closed roof or top wall 16.

The heating tubes 18 are generally disposed within the furnace chamber delineated by these walls and suitable heating means such asv gas or oil or similar burners 20 are placed in the floor, and as particularly contemplated herein, are also mounted at 2,2, in the end walls.

It is well known that heaters of this type may be suitably supported by columns 24 and a rain shed 26 is also provided. The furnace walls may be provided with suitable insulating iire brick indicated at 28 and, if desired, the walls may be of separate panel unit construction such as described inthe Reed et al. Patent 2,147,609. The products of combustion pass to a stack (not shown) interconnected with the gas discharge outlet 30m a well-known manner. While the unit shown is complete, it may be one unit of a multiplechamber ICC heater where added chambers are found preferable to the construction of larger chambers.

Our invention is primarily concerned with a heating tube arrangement whereby most effective pyrolysis can be obtained. In designing heaters for preheating or cracking hydrocarbons especially for cracking gases at high temperatures, it is important to have uniform heat transfer rates about the entire circumference of the tube surface. This is particularly true in the zones Where the reaction or conversion takes place and it has been customary in the past to use molten metal baths which, of course, have many operating objections.

In the usual types of tubular heaters, especially in the petroleum cracking field, it is found that one side ofthe tube is relatively colder than the other. With gas cracking, some coke formation is likely to occur on., the colder surface of the tube. Furthermore, Where the tube skin temperatures vary around the entire periphery of the tube, there is often degradation and decomposition of the heated medium on the side of the tube where the temperature is considerably above the average. If the temperature is below average, then there is a reduction in conversion yields.

Unequal rates of heat transfer on the circumference` of the tube also have the undesirable effect of increasing the tube stresses on the hot side particularly when the heat rates at operating temperature levels are of a high order of magnitude.

A further factor enters into the cracking of light hydrocarbons for the production of olefins such as ethylene, propylene, butylene, or in cracking or pyrolysis of organic compounds for production of rawV materials for chemicals and that is the control of the residence time at specified temperature and pressure conditions. It isl essential that provision be made for the variation of the residence time for different stocks for it is essential that the heaters be arranged to provide optimum residence time and heat rate inputs for the specified product as well as for different charge materials.

In our construction, we provide independently fired reaction and preheater sections so arranged as to give such flexibility of operating conditions that the shape of the temperature curve and the duration of soaking time may be changed at will to meet the requirements for optimum yields of varied products from a wide range of feed stocks.

In accordance with our invention we have adapted a type of tubular heater having baffle tile and roof tubes With cooperating plenum chamber as shown in the Reed Reissue Patent 21,396 to accomplish a highly efficient pyrolysis of hydrocarbons or organic compounds. As shown in Fig. 1, the preferred heater includes a preheater section and two reaction sections, The reaction sections each have a series of horizontally disposed serially connected bare surface tubes 34 opposite the burners 20, and to provide independent controlled reaction sections a bridge wall 36 may be provided between them. The reaction sections are completed by a series of horizontal roof tiles 38 which cooperate with the upper tubes 34 as will be hereinafter described.

Referring to Fig. 2, it will be noted that the tubes 34 are centered in arcuate substantially parabolic surface sections 3861 and 38b of adjacent tile immediately above the tubes. The arcuate surfaces 88a and 38h are not only of the desired shape to focus the heat rays on to the upper surface of the tubes 34 and are suitably spaced above the tubes (having a radius from 1.75 to l0 times the tube radius) to accomplish this purpose, but they also serve to direct, uniformly, the combustion products through the openings 38e into the preheater section above. These tile thus form a horizontal partition between the two chambers and are made of special refractory material both to establish draft resistance, and to effect a uniform and guided passage of the gases over the heat absorbing surface of the tubes. They thus provide the desired convection, and reradiation heat to the tubular heating surface and make it possible to have substantially uniform heat input throughout the 360 of the tube cross section as well as throughout its length.

Preheating of the charge isk accomplished in thepreheater section which not only has the side wall tubes 18 but preferably has two rows of roof tubes 40 and 41 the upper of which is provided with roof tiles 4Z to form a diilusion baille for the discharge of the products of combustion to the plenum chamber 44. These tiles may be of the type shown in the Zimmerman Patent 2,147,610.

To avoid local overheating of the tubes 18 due to laning or channelling of the low velocity heating gases relative thereto, this diifusion baille is arranged at the outer side of the row of tubes 41 with the gas flow passages 42a therein uniformly distributed and of less aggregate ilow area than the aggregate intertube area of the subjacent portions of the row of tubes 4l, thereby providing a pressure drop between opposite sides of the baille which will cause the low velocity heating gases to ilow uniformly past all of the tubes in both rows.

This baille performs two functions-it presents a restricted area for the outlet of the hot gases which insures slow travel of the combustion gases through the furnace proper particularly past the roof tubes; it also distributes the openings uniformly over the entire baille surface, thus providing a uniform ilow of heating gases across the roof tubes.

It will thus appear that the primary products of combustion leaving the reaction section below the horizontal partition 38 will pass up into the preheater section above and be further heated by the burners 22 and, by use of the baille tile 42 and plenum chamber 44, a blanketing eifect will be obtained which will provide substantially uniform heat input to all of the tubes in the side and roof of the preheater section.

In the construction which has been described the transfer of heat to the tubes 1S in the preheater section takes place substantially entirely by radiation. The travel of the combustion gases takes place at such a rate that very little convection eifect results. The tubes in the roof of the furnace (or in the exit side, where the gases do not leave the furnace at the roof) are spaced at sufilcient intervals to prevent a rapid ilow of gases past the lower row of tubes. The restricted exit areas in the diusion baille above the roof tubes are such as to prevent rapid passage of gases past these tubes, and also such as to insure a uniform distribution of the gases across the roof tubes. The result is a heat transfer wherein convection plays a very slight part except in the second row of roof tubes as explained above. The upper row of tubes 4l, of course, will be heated both by radiation and by reradiation and by convection eilfect.

It is also possible to include iloor tubes 46 which will be heated by radiation from the burners 22 as well as by the convection eilect of the gases passing up through the tile 33.

It will be obvious that this form of heater lends itself easily to a two-stream parallel flow of iluid through the heater, the heating in the two streams being at a substantially uniform and equal rate and to the same ilnal temperature throughout. Thus one stream may ilow serially through half the tubes 4l, half of the tubes 40, and one group of wall tubes 18 and half of the iloor tubes 46 and thence through half the reaction tubes 34 while the other stream llows through the remaining half of the heating surface. At the floor tubes 46, the ilow may be split and thence into four groups of tubes 34 in the reaction section and thence out the outlets 48a, Sb and 48C and 48d.

The time of reaction for pyrolysis of hydrocarbon gases and organic chemicals is frequently very short and may be in the order of a fraction of a second. The pressures are also quite low, the discharge pressure being substantially atmospheric and the inlet pressure is as low as possible to accomplish the movement of the products through the heater. Temperatures on the other hand are frequently in the high range of 1350 to 1450 F. and heat input rates may vary from 5000 to 15,000 B. t. u. per square foot per hour.

Specific examples of important uses for a heater of this type include the pyrolysis of propane, ethane, propylene and other light hydrocarbons to produce lighter oleiins and it may also be used in the organic chemical iield as, for example, in the pyrolysis of acetone to ketene. As will be appreciated, such applications depend upon very precise control and time-temperature relations to obtain optimum yields of the desired end products.

While we have shown and described a preferred form of embodiment of our invention, we are aware that modiilcations may be made thereto and we therefore contemplate that such modifications as come within the scope and spirit of the description herein and the claims appended hereinafter are within the contemplation of our invention.

We claim:

1. A iluid heater comprising means for forming a furnace chamber having a combustion gas exit including the major portion of the area of the upper side of the cham ber, means for conducting combustion within said chamber, a series of substantially parallel and substantially spaced fluid-heating roof tubes within said chamber and disposed for direct radiant-heating by said combustion around the forward portion of their circumferential surface facing the combustion, and a baille wall structure of heat resistant and reradiating material extending across said exit opposed to the rear portion of the circumferential surface of said tubes and having gas exit openings along the tubes and spaced directly back of them, said gas exit openings being substantially narrower than the diameter of the tubes, said baille wall structure having at the underside thereof pairs of curved heat-reilecting surfaces spaced entirely above the adjacent individual roof tubes and extending therealong and diverging transversely from said exit openings and toward the tubes whereby each pair together form a substantially parabolic arc around the back of the respective tube, the cross sectional width of said surfaces of the pairs being substantially greater than the diameter of the tubes and sufficient for said surfaces to intercept a predominant amount of the radiant heat directed toward the spaces between the tubes and the surfaces being disposed to reradiate and reilect said intercepted heat upon substantially the entire rear portion of the circumferential area of the tubes and also direct the combustion gases in convering streams around the back of the tubes to said exit openings, for nearly uniform distribution of heat around the entire tube circumference.

2. A iluid heater comprising means for forming a furnace chamber having a combustion gas exit including the major portion of the area of one of thel boundary walls thereof, means for conducting combustion within said chamber, a series of substantially parallel and substantially spaced fluid-heating tubes extending across said exit within said chamber and disposed for direct radiantheating by said combustion around the forward portion of their circumferential surface facing the combustion, anda bafile wall structure of heat resistant and reradiating material extending across said exit opposed to the rear portion of the circumferential surface of said tubes and having gas exit openings along the tubes and spaced directly back of them, said gas exit openings being substanstantially parabolic arc around the back of the respective exit openings, for nearly uniform distribution of heat tube, the cross sectional width of said surfaces of the around the entire tube circumference.

pairs being substantially greater than the diameter of the tubes and sufficient for said surfaces to intercept a pre- References Cited in the le 0f this Patent dominant amount of the radiant heat directed toward the 5 UNITED STATES PATENTS spaces between the tubes and the surfaces being disposed to reradiate and reflect said intercepted heat upon sub. /[mkllnermanl FJeb' 14 stantially the entire rear portion of the circumferential e er et a une 9 area of the tubes and also direct the combustion gases in FOREIGN PATENTS converging streams around the back of the tubes to said 10 242,198 Great Britain Nov. 5, 1925 

